This invention relates to methods of continuously degassing water, and more particularly to a method of degassing water in which heating energy can be economically used and a large amount of gaseous component can be continuously degassed from water in a relatively short time.
Heretofore, with a coating device, especially with a photographic photo-sensitive material coating device, a problem exists with bubbles of air or other gases included in coating liquid delivering lines, generally conduit pipes, connectors, filters, meters, etc. being stuck on the surface of a material to be coated, together with the coating liquid. This tends to considerably degrade the quality of the surface of the material coated therewith, since a smooth finish cannot be obtained. The trouble is due to the bubbles that occur in a concentrated manner immediately after the start of coating. As a result of an investigation of the cause for and the counter-measures to prevent this trouble, a method as described in the specification of Japanese Patent application Laid-Open No. 65824/1974 has been proposed. In the method, while a coating operation is suspended, the liquid delivering line is filled with a degassed cleaning liquid or water thereby to prevent the entry of a large amount of gas into the liquid delivering line. The degassed cleaning liquid is continuously supplied and discharged to remove the gas which is left in the liquid delivering line and the degassed cleaning liquid is replaced by the coating liquid immediately before the start of the coating operation in such a manner that the former liquid is followed by the latter liquid. This method contributes greatly to the prevention of the occurrence of the above-described trouble.
However, the difficulties encountered due to the bubbles, which are produced immediately after the start of the coating operation, is not completely overcome by the replacement of the cleaning liquid with the coating liquid. Especially, if the cleaning liquid itself is not completely degassed, the effect of the liquid replacement is considerably lessened. Accordingly, an improved method of degassing the cleaning liquid has been the subject of continuing study and development.
The following conventional methods of degassing a cleaning liquid or cleaning water are also available and known within the prior art:
(1) The so-called "heating type degassing method" in which the cleaning liquid or the cleaning water supplied into a heating tank is heated by a heat exchanger such as an electrical heater, a steam coil, or the like to a relatively high temperature, for instance 90.degree. C.-100.degree. C. so that gases melted in the liquid or water can be readily removed. PA1 (2) A pressure reduction type degassing method in which while the pressure of a liquid storing tank is reduced, the liquid or water is allowed to fall like rain to thereby degass it. PA1 (3) An ultrasonic type degassing method in which the liquid or water in a liquid storing tank is vibrated by ultrasonic waves to remove gases melted therein.
These conventional methods have been extensively employed; however; they are still disadvantageous in the following points:
In the heating type degassing method, the liquid or water is substantially heated to its boiling point by utilizing the fact that the solubility of gas in liquid or water changes in inverse proportion to the temperature of the liquid or water. Therefore, it is necessary to use a large amount of heating energy. In the case where the liquid or water should be at a low temperature when used in the practical application, it is necessary to decrease the temperature of the liquid or water to the required value for utilization. This increases manufacturing steps and effective processing times.
In the pressure reduction type degassing method, the device for practicing the method is bulky and intricate. The cost of the equipment is expensive, except for the case where a small amount of liquid or water is batchwise processed.
The ultrasonic type degassing method suffers from a drawback in that its capacity is insufficient for a tank having a large capacity and a liquid delivering line having a high flow rate.